Article 17 by Rodolfo Coccioni1*, Alessandro Montanari2, David Bice3, Henk Brinkhuis4, Alain Deino5, Fabrizio Frontalini1, Fabrizio Lirer6, Patrizia Maiorano7, Simonetta Monechi8, Jörg Pross9, Pierre Rochette10, Leonardo Sagnotti11, Marianna Sideri1, Mario Sprovieri12, Fabio Tateo13, Yannick Touchard10, Stefaan Van Simaeys14, and Graham L. Williams15 The Global Stratotype Section and Point (GSSP) for the base of the Chattian Stage (Paleogene System, Oligocene Series) at Monte Cagnero, Italy 1 Dipartimento di Scienze Pure e Applicate (DiSPeA) dell’Università degli Studi “Carlo Bo,” Campus Scientifico, Località Crocicchia, 61029, Urbino, Italy; *Corresponding author, E-mail: [email protected] 2 Osservatorio Geologico di Coldigioco, 62020 Frontale di Apiro, Italy 3 Department of Geosciences, the Pennsylvania State University, University Park, Pennsylvania 16802, USA 4 Laboratory of Palaeobotany and Palynology, Utrecht University, Budapestlaan 4, 3584 CD Utrecht, The Netherlands 5 Berkeley Geochronology Center, 2453 Ridge Road, Berkeley, California 94709, USA 6 Istituto per l’Ambiente Marino Costiero (IAMC-CNR), Calata Porta di Massa, Interno Porto di Napoli, 80123 Napoli, Italy 7 Dipartimento di Scienze della Terra e Geoambientali dell’Università degli Studi di Bari, Via Orabona 4, 70125 Bari, Italy 8 Dipartimento di Scienze della Terra dell’Università degli Studi di Firenze, Via La Pira 4, 50121 Firenze, Italy 9 Paleoenvironmental Dynamics Group, Institute of Earth Sciences, University of Heidelberg, Im Neuenheimer Feld 234, 69120 Heidelberg, Germany 10 Université d’Aix Marseille 3, UMR CNRS 6635, CEREGE Europole de l’Arbois BP80 13545 Aix en Provence Cedex 4, France 11 Istituto Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata 605, 00143 Roma, Italy 12 Istituto per l’Ambiente Marino Costiero (IAMC-CNR), Via del Mare 3, 91021 Torretta Granitola, Italy 13 Dipartimento di Geoscienze e Georisorse-CNR, Via Gardenigo 6, 35131 Padova, Italy 14 Exxon Mobil Upstream Research Company 22777 Springwood Village Pkwy, EMHC S1.2B.315 Houston, TX 77389, USA 15 Geological Survey of Canada, Bedford Institute of Oceanography, PO Box 1006, Dartmouth, Nova Scotia, B2Y 4A2, Canada (Received: April 11, 2017; Revised accepted: August 24, 2017) http://dx.doi.org/10.18814/epiiugs/2018/v41i1/018003 The GSSP for the base of the Chattian Stage (Paleogene southern part of the North Sea basin (e.g., Berggren, 1971; Hardenbol System, Oligocene Series) is defined at meter level 197 in and Berggren, 1978; Van Simaeys et al., 2004). Chronostratigraphi- the Monte Cagnero section, which belongs to the pelagic cally meaningful calcareous plankton is sparse in the generally mar- succession of the Umbria–Marche basin (Urbania, central ginal marine sedimentary environment of the historical reference Italy: 43°38′47.81″N–12°28′03.83″E). This level with an astro- sections, paleomagnetic signals are poor, and radiometrically datable nomical age of 27.82 Ma coincides with the highest common volcanic horizons are absent. Therefore, the historical type localities occurrence of the planktonic foraminifer Chiloguembelina do not represent suitable and continuous sections for the GSSP that comprises the Rupelian/Chattian boundary. Accordingly, a continu- cubensis at the base of planktonic foraminiferal O5 Zone and ous, well-calibrated base Chattian GSSP section offering good cor- falls in the upper part of calcareous nannofossil NP24 Zone, in relation potential has to be sought outside the North Sea basin. the lower part of dinocyst Dbi Zone, and in the lower Chron In search of a continuous section as GSSP of the Rupelian/Chattian C9n. The proposal was approved by the International boundary, the Oligocene Integrated Stratigraphy (OLIS) Working Subcommission of Paleogene Stratigraphy in July 2015, Group was formed to provide an integrated stratigraphy of the pelagic approved by the International Commission of Stratigra- Scaglia Cinerea Formation in the Umbria–Marche (U–M) region of phy in August 2016, and ratified by the International Union central Italy (Coccioni et al., 2008; Pross et al., 2010), which spans of Geological Sciences in September 2016. the uppermost Eocene through the entire Oligocene. Of the three sec- tions identified and studied to verify regional correlations – the Con- tessa Barbetti Road (CBR) near Gubbio, and Pieve d’Accinelli (PAC) Introduction near Piobbico, and Monte Cagnero (MCA) near Urbania (Coccioni et al., 2008) – the latter was selected to define the basal Chattian Stage The Rupelian and Chattian historical stratotypes were respectively GSSP (Fig. 1). located in northwestern Belgium and northwestern Germany, in the Episodes Vol. 41, No. 1 18 Figure 1. (a) Simplified roadmap of the Umbria–Marche region with the location of the Oligocene sections of Contessa Barbetti Road (CBR), Pieve d’Accinelli (PAC), and Monte Cagnero (MCA); (b) Precise location of the MCA section; (c) Location of the MCA section on an Oligo- cene paleogeographic map simplified and slightly amended from Dercourt et al. (1993). hard limestone layers protruding out of recessive, softer marls (Fig. Location and Geological Setting 4a). These calcareous benches are organized in cycles with a mean wavelength of about 5.6 m, as revealed by a band pass filtered curve The 86-m-thick MCA section is located on the southeastern slope obtained from a high-resolution magnetic susceptibility series, where of Monte Cagnero (727 m above sea level; coordinates: 43°38′47.81″N– low susceptibility represents calcareous marls and marly limestones, 12°28′03.83″E), a few kilometers to the SW of the town of Urbania and high susceptibility represents marls with a higher terrigenous (Fig. 1b) (Coccioni et al., 2008). (magnetic) content (Fig. 4a). The GSSP for the base of the Chattian Stage is The MCA section consists of a rhythmic alternation of gray-bluish, located at the highest common occurrence (HCO) of the planktonic pelagic marls, calcareous marls and marly limestones belonging to the foraminifer Chiloguembelina cubensis, i.e., the O4/O5 planktonic for- Scaglia Cinerea Formation whose carbonate component is mainly aminiferal zonal boundary of Wade et al. (2011), at meter level 197, thirty made up of planktonic foraminiferal tests and calcareous nannofos- cm below the base of a prominent calcareous bed within an otherwise sils, and the siliciclastic component is represented by terrigenous clay recessive, relatively thick marly interval (Figs. 2 and 4b). and silt (Fig. 2). The MCA section is free of turbidites and any other manifestation of basinal instability. Rare intercalations of thin, biotite- Biostratigraphy and Paleodepth rich volcano-sedimentary horizons are found and provide the means for direct radioisotopic dating of the magnetobiostratigraphy (Coc- The pelagic sediments of the MCA section contain abundant cal- cioni et al., 2008, and references therein) (Fig. 2). careous nannofossils and planktonic foraminifera, with common ben- thic foraminifera and rare ostracods. Palynomorphs are abundant as Stratigraphy well. Macrofossils were not found. Ichnofossils are common and mainly represented by Zoophycos and Planolites. The MCA section as GSSP for the base of the Chattian Stage (Fig. 2) is the continuation of the underlying upper Priabonian to middle Planktonic foraminifera Rupelian section, whose integrated stratigraphy and astrochronologic calibration were determined by Hyland et al. (2009). However, while Planktonic foraminiferal analysis is based on 173 samples col- working on the Rupelian to Chattian portion of the section, carefully lected at an average sampling resolution of 50 cm (Fig. 2) that corre- re-checking the stratimetry of Hyland et al. (2009), we found an error sponds to ~37.5 kyr and processed to obtain washed residues greater of one meter in the measured thickness at about meter level 125, in a than 32 µm using standard micropaleontological techniques. Plank- stretch of the section that crosses, for a few meters, a dirt road. Conse- tonic foraminiferal assemblages are rich, diverse, and well preserved quently, we had to add one meter to the section of Coccioni et al. throughout the section. The planktonic foraminiferal standard zona- (2008) (Fig. 2). A stratigraphic synthesis of the GSSP section of MCA tion of Wade et al. (2011) was applied, with the taxonomy of Paraglo- is shown in Figure 3, and described in detail below. borotalia opima and Paragloborotalia nana assessed following the taxonomic size-based concepts established by Wade et al. (2016). Pri- Lithostratigraphy mary and secondary events were recognized throughout O2 to O6 Zones (Figs. 2, 3, and 5; Table 1). The rhythmic bedding of the pelagic Scaglia Cinerea Formation is A progressive giantism of P. opima with increasing abundance of clearly manifested in the well-exposed southeastern slope of Monte the larger forms from the lower part of Chron C10n to the lower part Cagnero as a stepped topography, with prominent benches formed by of Chron C9n was recognized by Wade et al. (2016) through the mid- late Oligocene at Site U1334 (eastern equatorial Pacific Ocean). A March 2018 19 peak size of 680 µm is recorded in the lower part of Chron C9n very close (~2 m apart) to the Top occurrence of C. cubensis that accord- ing to King and Wade (2017) represents the highest (last) occurrence of this species. Fol- lowing this peak, the maximum size of P. opima decreases with its extinction event that marks the base of the late Oligocene Zone O6. Interestingly, a very similar pattern in abun- dance and